Air pollution control system and method

ABSTRACT

SO x  removal equipment for reducing sulfur oxides from flue gas from a boiler, a cooler which is provided on a downstream side of the SO x  removal equipment for reducing the sulfur oxides that remain in the flue gas and for decreasing a gas temperature, CO 2  recovery equipment which includes a CO 2  absorber, and an absorption liquid regenerator, and mist generation material reduction equipment for reducing a mist generation material which is a generation source of mist that is generated in the CO 2  absorber of the CO 2  recovery equipment before introducing the flue gas to the CO 2  recovery equipment are included.

FIELD

The present invention relates to an air pollution control system andmethod that reduce CO₂ from flue gas.

BACKGROUND

In recent years, the greenhouse effect due to CO₂ is indicated as one ofcauses of the global warming phenomenon, and the countermeasures thereofbecome an internationally urgent matter to protect the globalenvironment. CO₂ generation sources reach all human activity fields inwhich fossil fuels are burned, and there is a tendency to furtherstrengthen the demand for suppression of the discharge thereof. Forthis, for a power generation facility such as a thermal power plant thatuses a large amount of fossil fuels, a method of bringing combustionflue gas of an industrial facility such as a boiler or a gas turbineinto contact with an amine-based CO₂ absorption liquid to reduce andrecover CO₂ from the combustion flue gas and an air pollution controlsystem which stores the recovered CO₂ without emission to air has beenenergetically researched.

CO₂ recovery equipment which has, as the process of reducing andrecovering CO₂ from the combustion flue gas using a CO₂ absorptionliquid as described above, a process of bringing the combustion flue gasinto contact with the CO₂ absorption liquid in a CO₂ absorber(hereinafter, also simply referred to as “absorber”), and a process ofheating the CO₂ absorption liquid that absorbs CO₂ in an absorptionliquid regenerator (hereinafter, also simply referred to as“regenerator”) to emit CO₂ and regenerate the CO₂ absorption liquid soas to be circulated through the CO₂ absorber to be reused, is proposed(for example, Patent Literature 1).

In the CO₂ absorber, through countercurrent contact using an amine-basedCO₂ absorption liquid such as alkanolamine, CO₂ in the flue gas isabsorbed by the CO₂ absorption liquid in a chemical reaction (exothermicreaction), and the flue gas from which CO₂ is reduced is emitted to theoutside of the system. The CO₂ absorption liquid that absorbs CO₂ isalso called a “rich solution”. The rich solution is pressurized by apump, is heated in a heat exchanger by a high-temperature CO₂ absorptionliquid (lean solution) regenerated as CO₂ is emitted in the regenerator,and is supplied to the regenerator.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Laid-open Patent Publication No. 3-193116

SUMMARY Technical Problem

However, in the air pollution control system, in a case where a mistgeneration material that is a generation source of mist generated in theabsorber of the CO₂ recovery equipment is included in the flue gasintroduced to the CO₂ absorber that absorbs CO₂ in the CO₂ recoveryequipment, there is a problem in that the CO₂ absorption liquid isentrained by the mist generation material and thus the amount of CO₂absorption liquid that scatters to the outside of the system isincreased.

Such a case, where the scattering of the CO₂ absorption liquid to theoutside of the system occurs, is connected to a significant loss of theCO₂ absorption liquid, and an unnecessary amount of the CO₂ absorptionliquid has to be replenished. Therefore, the scattering of the CO₂absorption liquid to the outside of the system needs to be suppressed.

Here, the establishment of an air pollution control system whichsuppresses the scattering of a CO₂ absorption liquid from a CO₂ absorberis desired.

In order to solve the problem, an object of the present invention is toprovide an air pollution control system and method capable ofsignificantly reducing entraining of a CO₂ absorption liquid when fluegas from which CO₂ is reduced is discharged to the outside of a system,and performing an appropriate air pollution control.

Solution to Problem

According to a first aspect of invention in order to solve the aboveproblems, there is provided an air pollution control system including:SO_(x) removal equipment which reduces sulfur oxides from flue gas froma boiler; a cooler which is provided on a downstream side of the SO_(x)removal equipment so as to reduce the sulfur oxides that remain in theflue gas and decrease a gas temperature; CO₂ recovery equipment whichincludes a CO₂ absorber for bringing CO₂ in the flue gas into contactwith a CO₂ absorption liquid so as to be reduced, and an absorptionliquid regenerator for causing the CO₂ absorption liquid to emit CO₂ soas to recover CO₂ and regenerate the CO₂ absorption liquid; and mistgeneration material reduction equipment which reduces a mist generationmaterial which is a generation source of mist that is generated in theCO₂ absorber of the CO₂ recovery equipment before introducing the fluegas to the CO₂ recovery equipment.

According to a second aspect of the present invention, there is providedthe air pollution control system according to the first aspect, furtherincluding: NO_(x) removal equipment which reduces nitrogen oxides fromthe flue gas; and a dry type electric dust collector which reducesparticulates.

According to a third aspect of the present invention, there is providedthe air pollution control system according to the second aspect, whereinthe mist generation material reduction equipment is a sodium bisulfiteinjection equipment which injects sodium bisulfite between the NOremoval equipment and the electric dust collector for reducing the mistgeneration material in a gas state from the flue gas.

According to a fourth aspect of the present invention, there is providedthe air pollution control system according to the second aspect, whereinthe mist generation material reduction equipment is an ammonia injectionequipment which injects ammonia to an upstream side of the electric dustcollector for reducing the mist generation material in a gas state fromthe flue gas.

According to a fifth aspect of the present invention, there is providedthe air pollution control system according to the second aspect, whereinthe mist generation material reduction equipment is a dissolved saltspraying equipment which sprays a dissolved salt between the electricdust collector and the SO_(x) removal equipment for reducing the mistgeneration material in a gas state from the flue gas.

According to a sixth aspect of the present invention, there is providedthe air pollution control system according to the first or secondaspect, wherein the mist generation material reduction equipment is awet type electric dust collector which is provided on any of an upstreamside and a downstream side of the cooler for reducing particulates thatremain in the flue gas and reducing the mist generation material in amist state from the flue gas.

According to a seventh aspect of the present invention, there isprovided the air pollution control system according to the first orsecond aspect, wherein the mist generation material reduction equipmentis a wet type electric dust collector-integrated cooler which has a wettype electric dust collection unit for reducing particulates that remainin the flue gas therein so as to reduce the mist generation material ina mist state from the flue gas.

According to an eighth aspect of the present invention, there isprovided the air pollution control system according to the first orsecond aspect, wherein the mist generation material reduction equipmentis a demister which is provided at a top portion of the cooler to reduceparticulates that remain in the flue gas therein and reduce the mistgeneration material in a mist state from the flue gas.

According to a ninth aspect of the present invention, there is providedthe air pollution control system according to the first or secondaspect, wherein the mist generation material reduction equipmentincludes a first heat exchanger which is provided on an upstream side ofthe SO_(x) removal equipment to decrease a temperature of the flue gasand calcium carbonate spraying equipment which sprays calcium carbonatebetween the first heat exchanger and the electric dust collector forconverting the mist generation material in the flue gas from a gas stateto a mist state and neutralizing the mist generation material in themist state using calcium carbonate so as to be reduced.

According to a tenth aspect of the present invention, there is providedthe air pollution control system according to the second aspect, whereinthe mist generation material reduction equipment includes a second heatexchanger which is provided on an upstream side of the electric dustcollector to decrease a temperature of the flue gas for converting themist generation material in the flue gas from a gas state to a miststate and causing the mist generation material in the mist state toadhere to the particulates so as to be reduced by the dry type electricdust collector.

According to an eleventh aspect of the present invention, there isprovided the air pollution control method including: on an upstream sideof CO₂ recovery equipment which brings CO₂ in flue gas into contact witha CO₂ absorption liquid so as to be absorbed and reduced,

reducing a mist generation material in any of a gas state and a miststate from the flue gas generated in a boiler; and decreasing an amountof the mist generation material in the flue gas introduced to the CO₂recovery equipment to a predetermined amount or less.

Advantageous Effects of Invention

According to the air pollution control system of the present invention,since the mist generation material reduction equipment is providedbefore the introduction to the CO₂ recovery equipment, the amount ofmist generation material in the flue gas when being introduced to theCO₂ absorber is significantly decreased. As a result, the amount of CO₂absorption liquid that is entrained by mist and scatters to the outsideof the system is decreased. Therefore, the loss of the CO₂ absorptionliquid that scatters to the outside of the system may be significantlydecreased, and an increase in running cost during the air pollutioncontrol may be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an air pollution control system of anembodiment according to the present invention.

FIG. 2 is a conceptual diagram of a mechanism of mist generation.

FIG. 3-1 is a photograph illustrating a state where white smoke isdecreased in a CO₂ absorber.

FIG. 3-2 is a photograph illustrating a state where white smoke isgenerated in the CO₂ absorber.

FIG. 4-1 is a schematic diagram of an air pollution control systemaccording to Embodiment 1.

FIG. 4-2 is a schematic diagram of another air pollution control systemaccording to Embodiment 1.

FIG. 5 is a schematic diagram of an air pollution control systemaccording to Embodiment 2.

FIG. 6 is a schematic diagram of an air pollution control systemaccording to Embodiment 3.

FIG. 7 is a schematic diagram of an air pollution control systemaccording to Embodiment 4.

FIG. 8 is a schematic diagram of an air pollution control systemaccording to Embodiment 5.

FIG. 9 is a schematic diagram of an air pollution control systemaccording to Embodiment 6.

FIG. 10 is a schematic diagram of an air pollution control systemaccording to Embodiment 7.

FIG. 11 is a schematic diagram of an air pollution control systemaccording to Embodiment 8.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to the drawings. Note that, the present invention is notlimited by embodiments and examples. In addition, components in theembodiments and the examples include those that may be easily assumed bythose skilled in the art or are practically the same.

FIG. 1 is a schematic diagram of an air pollution control system of anembodiment according to the present invention.

As illustrated in FIG. 1, in an air pollution control system 10 of theembodiment according to the present invention, flue gas 12 from a boiler11 is subjected to a reduction in nitrogen oxides (NO_(x)) from the fluegas 12 by NO_(x) removal equipment 13, and thereafter is first guided toan air heater AH to heat air supplied to the boiler 11. Thereafter, theflue gas 12 is introduced to a dry type electric dust collector 14 whichis dust reduction equipment so as to reduce particulates. Next, the fluegas 12 is introduced to SO_(x) removal equipment 15 to reduce sulfuroxides (SO_(x)). Then, the flue gas 12 is cooled by a cooler 16, isthereafter introduced to CO₂ recovery equipment 17 to reduce carbondioxide, and purified gas 18 is emitted from the top portion of a CO₂absorber to the air which is outside the system. Note that, theparticulates reduced by the electric dust collector 14 are subjected toan additional ash treatment 14 a.

In the present invention, before introducing the flue gas 12 to the CO₂recovery equipment 17, mist generation material reduction equipment 20which reduces a mist generation material that is a generation source ofmist generated in the CO₂ absorber of the CO₂ recovery equipment 17 isprovided.

According to the air pollution control system 10 according to thepresent invention, since the mist generation material reductionequipment 20 is provided before the introduction to the CO₂ recoveryequipment 17, the amount of mist generation material in the flue gas 12when being introduced to the CO₂ absorber of the CO₂ recovery equipment17 is significantly decreased. As a result, the amount of CO₂ absorptionliquid (hereinafter, also referred to as “absorption liquid”) entrainedby mist and dispersed to the outside may be significantly decreased. Asa result, the loss of the absorption liquid that scatters to the outsideof the system is significantly decreased, and thus an unnecessaryreplenishment is eliminated, thereby suppressing an increase in runningcost during the air pollution control.

The mist generation material reduced by the mist generation materialreduction equipment 20 according to the present invention is SO₃ mist,nitric acid mist, hydrochloric acid mist, water vapor mist, or the likeand is referred to as a material that becomes a mist generation factorin the CO₂ absorber. Note that, equipment that performs a reduction in agas state before becoming mist is also included in the mist generationmaterial reduction equipment 20 according to the present invention.

Since the flue gas 12 from the boiler 11 is in a high-temperature state,the mist generation material is present in a gas state at first.Thereafter, in a process of passing through the electric dust collectorand the SO_(x) removal equipment, the flue gas is cooled, and thus themist generation material changes from the gas state to a mist state.

The particle size of the mist of the mist generation material in thepresent invention is referred to as a size of equal to or smaller than3.0 μm.

The form of mist generation and entraining of the absorption liquid inthe CO₂ absorber of the CO₂ recovery equipment 17 will be describedusing FIGS. 2, 3-1, and 3-2.

FIG. 2 is a conceptual diagram of a mechanism of entraining of theabsorption liquid by mist generation. FIG. 3-1 is a photographillustrating a state where white smoke is decreased in the CO₂ absorber,and FIG. 3-2 is a photograph illustrating a state where white smoke isgenerated in the CO₂ absorber. Although, SO₃ mist is exemplified as themist generation material in the description, descriptions with otherkinds of mist will be the same. The flue gas 12 from the boiler 11 issubjected to a gas purifying treatment such as NO_(x) removal, areduction in particulates, and SO_(x) removal, and the flue gas 12 iscooled by the cooler 16, resulting in a gas temperature of about 50° C.Since this temperature state is equal to or less than the acid dewpoint, there is SO₃ mist (for example, 0.1 to 1.0 μm).

A SO₃ mist 50 has SO₃ as a nucleus 51 and water vapor 52 that isincorporated into the periphery thereof.

In the CO₂ absorber, the absorption liquid is sprayed from nozzles andfalls, and the falling absorption liquid and the flue gas are subjectedto countercurrent contact such that CO₂ is absorbed by the absorptionliquid. On the other hand, the flue gas 12 is introduced from the lowerside of the CO₂ absorber and is discharged to the upper side. Here, theSO₃ mist 50 is not absorbed by the absorption liquid and ascends alongwith the gas stream of the flue gas 12.

Here, in the CO₂ absorber, when the absorption liquid is supplied fromthe nozzles, the absorption liquid falls and a part of the absorptionliquid and moisture evaporates, and thus a gaseous absorption liquid 41Gand water vapor 42 are generated.

In addition, the amount of gaseous absorption liquid 41G and the watervapor 42 further increases as the temperature of the absorption liquidis increased due to, for example, the exothermic reaction of theabsorption liquid when CO₂ is absorbed.

Then, the gaseous absorption liquid 41G and the water vapor 42 areincorporated into the SO₃ mist 50, resulting in a SO₃ mist (bloatedmist) 53 including a bloated (for example, about 0.5 to 2.0 μm)absorption liquid.

As described above, the SO₃ mist 50 in the flue gas 12, before beingintroduced to the CO₂ recovery equipment 17, incorporates the gaseousabsorption liquid 41G and the water vapor 42 in the CO₂ absorber,becomes the SO₃ mist 53 including the absorption liquid, and scattersfrom the top portion of the CO₂ absorber while being entrained by theflue gas 12. Therefore, the loss of the absorption liquid occurs.

The form of white smoke generation in the CO₂ absorber is illustrated inFIGS. 3-1 and 3-2.

FIG. 3-1 illustrates a case where the amount of mist generation materialis decreased to a predetermined amount or less by providing the mistgeneration material reduction equipment 20 for the flue gas 12introduced to the CO₂ absorber and a state where the scatting of the SO₃mist (bloated mist) 53 including the absorption liquid in the CO₂absorber is significantly reduced and thus generation of white smoke issuppressed. FIG. 3-2 illustrates a case where the flue gas 12 isintroduced as it is without providing the mist generation materialreduction equipment 20 for the flue gas 12 introduced to the CO₂absorber and a state where the scatting of the SO₃ mist (bloated mist)53 including the absorption liquid in the CO₂ absorber occurs and thuswhite smoke is generated.

That is, in the present invention, the mist generated in the CO₂absorber is referred to as the SO₃ mist (bloated mist) 53 including theabsorption liquid. Confirming the presence or absence of the generationof bloated mist is referred to as the presence or absence of generationof white smoke, and by suppressing the bloated mist in the CO₂ absorber,generation of white smoke is eliminated. Furthermore, the scattering ofthe absorption liquid is prevented.

In addition, regarding the bloated mist, as illustrated in FIG. 2, theremay be cases where the gaseous absorption liquid 41G and the gaseouswater vapor 42 are separately incorporated into the SO₃ mist 50 in theflue gas 12 in the CO₂ absorber to respectively form a SO₃ mist (bloatedmist) 53A including the absorption liquid and a SO₃ mist (bloated mist)53B including the water vapor.

Here, in the case of the mist (bloated mist) 53B including the watervapor, there is no loss of the absorption liquid. However, sincegeneration of white smoke of the purified gas 18 to be discharged to theoutside of a system occurs, a reduction in the mist generation materialis also needed.

Therefore, according to the present invention, by providing the mistgeneration material reduction equipment 20 before introduction to theCO₂ recovery equipment 17, entraining of the CO₂ absorption liquid maybe significantly reduced when the flue gas 12 from which CO₂ is reducedis discharged to the outside of the system, and an appropriate airpollution control may be performed.

Therefore, in the present invention, by providing the mist generationmaterial reduction equipment 20 that reduces the mist generationmaterial which is the generation source of the mist (the SO₃ mistincluding the absorption liquid which is the bloated mist) generated inthe CO₂ absorber of the CO₂ recovery equipment 17 before introducing theflue gas 12 to the CO₂ recovery equipment 17, the loss of the absorptionliquid that scatters to the outside of the system from the CO₂ absorbermay be significantly decreased.

The mist generation material reduction equipment 20 may be provided onthe upstream side of the dry type electric dust collector 14, betweenthe dry type electric dust collector 14 and the SO_(x) removal equipment15, or in either of the front and the rear of the cooler 16, or to beintegrated into the cooler 16.

Here, before introducing the flue gas 12 to the CO₂ recovery equipment17, it is preferable that the amount of SO₃ mist 50 be decreased to 3ppm or less for prevention of white smoke and prevention of scatteringof the absorption liquid in the CO₂ absorber. This is because when theamount of SO₃ mist 50 is decreased to 3 ppm or less, scatteringprevention is suppressed, and deterioration of, for example, anamine-based absorption liquid due to SO₃ is prevented.

According to the present invention, since the scattering of theabsorption liquid is prevented and the deterioration of the absorptionliquid is prevented, a decrease in the number of regeneration treatmentsperformed in the regeneration equipment (reclaiming equipment) for theabsorption liquid may be achieved, and the loss of the absorption liquidis further significantly decreased, so that a decrease in the amount ofthe replenished absorption liquid may be achieved. Therefore, the systemefficiency of the air pollution control system may be significantlyenhanced.

Note that, in this embodiment, the electric dust collector isexemplified as the dust reduction equipment in the description. However,the present invention is not limited to this as long as particulates arereduced from the flue gas 12, and besides the electric dust collector,for example, a bag filter or a venturi scrubber may be exemplified.

In the following embodiment, specific embodiments of the mist generationmaterial reduction equipment that reduces the mist generation materialwill be described.

Embodiment 1

The air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings. FIG. 4-1 is a schematic diagram of theair pollution control system according to Embodiment 1. FIG. 4-2 is aschematic diagram of another air pollution control system according toEmbodiment 1. Note that, in the following embodiments, SO₃ isexemplified as the mist generation material in the description, but thepresent invention is not limited thereto.

As illustrated in FIG. 4-1, an air pollution control system 10Aaccording to Embodiment 1 includes the NO_(x) removal equipment 13 whichreduces nitrogen oxides from the flue gas 12 from the boiler (forexample, coal-fired boiler) 11, the electric dust collector 14 which isprovided on the downstream side of the NO_(x) removal equipment 13 andreduces particulates from the flue gas 12, the SO_(x) removal equipment15 which is provided on the downstream side of the electric dustcollector 14 and reduces sulfur oxides from the flue gas 12, the cooler16 which is provided on the downstream side of the SO_(x) removalequipment 15 and has a cooling unit 16 a that decreases the gastemperature, and the CO₂ recovery equipment 17 which includes an CO₂absorber 17A that brings CO₂ in the flue gas 12 into contact with theabsorption liquid so as to be reduced and an absorption liquidregenerator 17B that causes the absorption liquid to emit CO₂ to recoverthe CO₂ and regenerate the absorption liquid.

In this embodiment, before introducing the SO₃ mist 50 to the CO₂recovery equipment 17, as a countermeasure for a reduction, sodiumbisulfite injection equipment 21 which injects sodium bisulfite (SBS;Sodium bisulfate) between the NO_(x) removal equipment 13 and theelectric dust collector 14 is provided. The sodium bisulfite injectionequipment 21 according to this embodiment functions as the mistgeneration material reduction equipment 20.

As a result, by supplying SBS into the flue gas 12 having a gastemperature of about 120° C. to 160° C. on the downstream side of theair heater AH, SO₃ in the gas state is reduced. As a result, the amountof the SO₃ mist 50 introduced to the CO₂ recovery equipment 17 isdecreased.

That is, in this embodiment, SBS is sprayed from the sodium bisulfiteinjection equipment 21 to convert SO₃ in the gas state to NaHSO₄ orNa₂SO₄ solids so as to be arrested thereafter by the dry type electricdust collector 14 along with particulates in the flue gas 12. The formof this reaction is shown as follows.

SO₃+NaHSO₃→NaHSO₄+SO₂  (1)

SO₃+2NaHSO₃→Na₂SO₄+2SO₂+H₂O  (2)

Note that, the particulates arrested by the electric dust collector 14are subjected to an ash treatment 14 a.

Injection of sodium bisulfite (SBS) may be performed anywhere on theupstream side of the electric dust collector 14, and for example, sodiumbisulfite (SBS) may be supplied between the NO_(x) removal equipment 13and the air heater AH (broken line in FIG. 4-1).

In addition, the flue gas 12 from which particulates are reduced in theelectric dust collector 14 is subjected to a reduction in sulfur oxidesfrom the flue gas 12 in the SO_(x) removal equipment 15, limestone(CaCO₃) 15 a and oxidation air 15 b are supplied to cause the reducedsulfur oxides to become gypsum 15 c through a limestone-gypsum method,and desulfurized waste water 15 d is additionally treated. Note that, inthe figures, reference numerals 17 a, 17 b, 17 c, 17 d, 17 e, and 17 fdenote a reboiler, saturated water vapor, condensed water, a separationdrum, recovered CO₂, and an absorption liquid heat exchanger,respectively.

The flue gas 12 desulfurized by the SO_(x) removal equipment 15 iscooled by the cooler 16 to cause the flue gas temperature to be 50° C.or less, and is introduced to the CO₂ recovery equipment 17 includingthe CO₂ absorber 17A and the absorption liquid regenerator 17B. Here,CO₂ in the flue gas 12 is reduced by, for example, the amine-basedabsorption liquid 41. At this time, in this embodiment, as a result ofreducing SO₃ in the gas state which is the mist generation material inthe flue gas 12, a decrease in the amount of the SO₃ mist 50 introducedto the CO₂ recovery equipment 17 is achieved. Therefore, the generationof white smoke of the purified gas 18 discharged from the CO₂ absorber17A, which is caused by the mist, is suppressed, and the entraining ofthe absorption liquid 41 is suppressed.

As a result, an air pollution control system in which the loss of theabsorption liquid 41 is significantly decreased may be provided.

Here, in this embodiment, the amine-based absorption liquid isexemplified as the absorption liquid 41. However, the absorption liquidof the present invention is not limited to the amine-based absorptionliquid. As the absorption liquid, besides the amine-based absorptionliquid, for example, an amino acid-based absorption liquid, an ionicliquid absorption liquid, a hot potassium carbonate absorption liquidmade of potassium carbonate and amines, and the like may be exemplified.

FIG. 4-2 is a schematic diagram of an air pollution control system of amodified embodiment of Embodiment 1. In the cooler 16 illustrated inFIG. 4-1, the flue gas 12 is cooled. However, as illustrated in FIG.4-2, a finishing SO_(x) removal unit 16 b is provided on the lower sideof the cooler 16, and the limestone (CaCO₃) 15 a and the oxidation air15 b are supplied to form the gypsum 15 c through the limestone-gypsummethod. Accordingly, sulfur oxides that remain in the flue gas 12 fromthe SO_(x) removal equipment 15 are reduced to further enhance theSO_(x) removal efficiency, and thus most of the residual sulfur oxidesmay be reduced. Note that, a strong alkaline agent such as sodiumhydroxide (NaOH) may be added instead of the limestone. In thisembodiment, in the finishing SO_(x) removal unit 16 b, a liquid columntype is used as a method of supplying a SO_(x) removal absorptionliquid. However, the present invention is not limited thereto, and anyof sprinkling type, jet type, and filling type may also be used.

Here, as the SO_(x) removal absorption liquid used in the finishingSO_(x) removal unit 16 b, besides the limestone (CaCO₃), a strongalkaline agent such as NaOH, Na₂CO₃, NaHCO₃, Ca(OH)₂, or Mg(OH)₂ may beexemplified. By using the strong alkaline agent, further enhancement ofthe SO_(x) removal performance may be achieved, and this is particularlyeffective in a case where the flue gas 12 having a high sulfur oxideconcentration is introduced, thereby decreasing the concentration ofsulfur oxides in the flue gas 12 introduced to the CO₂ recoveryequipment 17 to an extremely low concentration. The SO_(x) removalperformance is increased compared to the limestone-gypsum method.Therefore, even in a case where the concentration of sulfur oxides inthe introduced flue gas 12 is high, favorable SO_(x) removal performanceis exhibited, which is preferable.

Embodiment 2

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 5 is a schematic diagram of an air pollution control systemaccording to Embodiment 2. As illustrated in FIG. 5, the air pollutioncontrol system 10B according to Embodiment 2 is provided with ammoniainjection equipment 22 on the upstream side of the dry type electricdust collector 14 instead of the sodium bisulfite injection equipment 21used in Embodiment 1 so as to spray ammonia into the flue gas 12. Theammonia injection equipment 22 according to this embodiment functions asthe mist generation material reduction equipment 20.

On the upstream side of the electric dust collector 14, ammonia (NH₃)gas is sprayed to form ammonium sulfate (NH)₄SO₄ and this is arrested bythe dry type electric dust collector 14 along with particulates. In thisembodiment, as a result of reducing SO₃ in the gas state which is themist generation material from the flue gas 12, a decrease in the amountof the SO₃ mist introduced to the CO₂ recovery equipment 17 is achieved.Therefore, the generation of white smoke of the purified gas 18discharged from the CO₂ absorber 17A, which is caused by the mist, issuppressed, and the entraining of the absorption liquid 41 issuppressed. As a result, an air pollution control system in which thereis no loss of the absorption liquid 41 may be provided.

In a case where the NO_(x) removal equipment 13 is present on theupstream side of the air pollution control system, by increasing asupply amount of ammonia (NH₃) used in the NO_(x) removal equipment 13,an ammonia (NH₃) injection equipment does not need to be newly providedand may be replaced.

Embodiment 3

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 6 is a schematic diagram of an air pollution control systemaccording to Embodiment 3. As illustrated in FIG. 6, the air pollutioncontrol system 10C according to Embodiment 3 is provided with dissolvedsalt spraying equipment 23 between the dry type electric dust collector14 and the SO_(x) removal equipment 15 instead of the sodium bisulfiteinjection equipment 21 used in Embodiment 1 so as to spray a dissolvedsalt 24 into the flue gas 12. The dissolved salt spraying equipment 23according to this embodiment functions as the mist generation materialreduction equipment 20.

In this embodiment, an aqueous solution of the dissolved salt 24, whichis soluble, such as Na₂SO₄ and MgSO₄ is sprayed on the upstream side ofthe SO_(x) removal equipment 15. As the dissolved salt solution issprayed into the flue gas 12 having a gas temperature of, for example,about 130° C. to 150° C. on the downstream side of the dry type electricdust collector 14, fine dry dissolved salt particles are formed, and SO₃in the gas state is adsorbed and fixed onto the dissolved saltparticles, thereby reducing the SO₃ in the gas state from the flue gas12. As a result, the amount of the SO₃ mist 50 introduced to the CO₂recovery equipment 17 is decreased.

As the dissolved salt 24, for example, there are NaCl, NaOH, Na₂SO₄,Na₂CO₃, KCl, KOH, K₂SO₄, K₂CO₃, KHCO₃, MgCl₂, MgSO₄, CaCl₂, and thelike.

Here, when Na₂SO₄ is used as the dissolved salt 24, a reaction betweendissolved salt particles (Na₂SO₄) and SO₃ as in Expression (3) belowproceeds. As a result, NaHSO₄·H₂O (solid) is formed.

Na₂SO₄+SO₃+3H₂O→2NaHSO₄·H₂O  (3)

Both Na₂SO₄ and NaHSO₄·H₂O are soluble and thus are dissolved in theSO_(x) removal equipment 15 on the downstream side. Therefore, comparedto a case of Embodiment 2 in which ammonia is injected, a solid materialtreatment including ammonia of the dry type electric dust collector 14is unnecessary. In this embodiment, as a result of reducing SO₃ in thegas state which is the mist generation material from the flue gas 12, adecrease in the amount of the SO₃ mist 50 introduced to the CO₂ recoveryequipment 17 is achieved. Therefore, the generation of white smoke ofthe purified gas 18 discharged from the CO₂ absorber 17A, which iscaused by the mist, is suppressed, and the entraining of the absorptionliquid 41 is suppressed. As a result, an air pollution control system inwhich the loss of the absorption liquid 41 is significantly decreasedmay be provided.

Embodiment 4

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 7 is a schematic diagram of an air pollution control systemaccording to Embodiment 4. As illustrated in FIG. 7, the air pollutioncontrol system 10D according to Embodiment 4 is provided with a wet typeelectric dust collector 25 between the SO_(x) removal equipment 15 andthe cooler 16 instead of the sodium bisulfite injection equipment 21used in Embodiment 1. The wet type electric dust collector 25 accordingto this embodiment functions as the mist generation material reductionequipment 20. The wet type electric dust collector 25 may be provided onthe downstream side of the SO_(x) removal equipment 15 to charge andreduce the SO₃ mist 50 from the flue gas 12. In this embodiment, the wettype electric dust collector 25 is provided on the upstream side of thecooler 16 (between the SO_(x) removal equipment 15 and the cooler 16).However, the present invention is not limited thereto, and the wet typeelectric dust collector 25 may also be provided on the downstream sideof the cooler 16 (between the cooler 16 and the CO₂ recovery equipment17).

In this embodiment, as a result of reducing SO₃ in the mist state whichis the mist generation material in the flue gas 12, a decrease in theamount of the SO₃ mist 50 introduced to the CO₂ recovery equipment 17 isachieved. Therefore, the generation of white smoke of the purified gas18 discharged from the CO₂ absorber 17A, which is caused by the mist, issuppressed, and the entraining of the absorption liquid 41 issuppressed. As a result, an air pollution control system in which theloss of the absorption liquid 41 is significantly decreased may beprovided.

Embodiment 5

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 8 is a schematic diagram of an air pollution control systemaccording to Embodiment 6. As illustrated in FIG. 8, the air pollutioncontrol system 10E according to Embodiment 6 is provided with a wet typeelectric dust collection unit 25 a between the SO_(x) removal unit 16 band the cooling unit 16 a inside the cooler 16 of Embodiment 5 so as toconfigure a wet type electric dust collector-integrated cooler 27.Accordingly, finishing SO_(x) removal equipment that performs a finishof SO_(x) removal is constructed. The wet type electric dust collectionunit 25 a of the cooling unit 16 a according to this embodimentfunctions as the mist generation material reduction equipment 20.Compared to the system of Embodiment 4, it is unnecessary to separatelyinstall the wet type electric dust collector 25, and thus there is noneed to secure the installation space thereof.

In this embodiment, by configuring the wet type electric dustcollector-integrated cooler 27, the SO₃ mist 50 may be reduced from theflue gas 12. In this embodiment, as a result of reducing SO₃ in the miststate which is the mist generation material from the flue gas 12, adecrease in the amount of the SO₃ mist 50 introduced to the CO₂ recoveryequipment 17 is achieved. Therefore, the generation of white smoke ofthe purified gas 18 discharged from the CO₂ absorber 17A, which iscaused by the mist, is suppressed, and the entraining of the absorptionliquid 41 is suppressed. As a result, an air pollution control system inwhich the loss of the absorption liquid 41 is significantly decreasedmay be provided.

Embodiment 6

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 9 is a schematic diagram of an air pollution control systemaccording to Embodiment 6. As illustrated in FIG. 9, the air pollutioncontrol system 1OF according to Embodiment 5 is provided with a demister26 inside the cooler 16 instead of the sodium bisulfite injectionequipment 21 used in Embodiment 1. The demister 26 according to thisembodiment functions as the mist generation material reduction equipment20.

By providing the demister 26 at the top portion on the upper side of thedownstream of the cooling unit 16 a of the cooler 16, the SO₃ mist 50may be reduced from the flue gas 12. In this embodiment, as a result ofreducing SO₃ in the mist state which is the mist generation materialfrom the flue gas 12, a decrease in the amount of the SO₃ mist 50introduced to the CO₂ recovery equipment 17 is achieved. Therefore, thegeneration of white smoke of the purified gas 18 discharged from the CO₂absorber 17A, which is caused by the mist, is suppressed, and theentraining of the absorption liquid 41 is suppressed. As a result, anair pollution control system in which the loss of the absorption liquid41 is significantly decreased may be provided.

In this embodiment, the wire diameter of the wire mesh that constitutesthe demister 26 may be 1 to 20 μm, and more preferably 3 to 10 μm, butthe present invention is not limited thereto. In addition, it ispreferable that the void fraction of the demister 26 be about 90 to 97%,but the present invention is not limited thereto.

Embodiment 7

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 10 is a schematic diagram of an air pollution control systemaccording to Embodiment 7. As illustrated in FIG. 10, the air pollutioncontrol system 10G according to Embodiment 7 is provided with calciumcarbonate spraying equipment 31 between the electric dust collector 14and the SO_(x) removal equipment 15 instead of the sodium bisulfiteinjection equipment 21 used in Embodiment 1 so as to spray calciumcarbonate (CaCO₃) into the flue gas 12. In addition, on the upstreamside of the SO_(x) removal equipment 15 which is on the downstream sidewhere spraying is performed, a first heat exchanger 32 which decreasesthe flue gas temperature is provided. The calcium carbonate sprayingequipment 31 and the first heat exchanger 32 according to thisembodiment function as the mist generation material reduction equipment20.

On the upstream side of the SO_(x) removal equipment 15, as thetemperature of the flue gas 12 is decreased to a sulfuric acid dew pointor less by the first heat exchanger 32, gaseous SO₃ is converted tomist-like SO₃, and the mist-like SO₃ is neutralized by CaCO₃ (limestone)sprayed into the flue gas 12, thereby reducing the mist-like SO₃ fromthe flue gas 12.

In this embodiment, as a result of converting SO₃ which is the mistgeneration material in the flue gas 12 from the gas state to the miststate and reducing the mist-like mist generation material, a decrease inthe amount of the SO₃ mist 50 introduced to the CO₂ recovery equipment17 is achieved. Therefore, the generation of white smoke of the purifiedgas 18 discharged from the CO₂ absorber 17A, which is caused by themist, is suppressed, and the entraining of the absorption liquid 41 issuppressed. As a result, an air pollution control system in which theloss of the absorption liquid 41 is significantly decreased may beprovided.

Embodiment 8

An air pollution control system including the CO₂ recovery equipmentaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 11 is a schematic diagram of an air pollution control systemaccording to Embodiment 8. As illustrated in FIG. 11, the air pollutioncontrol system 10H according to Embodiment 8 is provided with a secondheat exchanger 33 which decreases the gas temperature of the flue gas12, on the upstream side of the dry type electric dust collector 14instead of the first heat exchanger 32 provided in Embodiment 7. Thesecond heat exchanger 33 according to this embodiment functions as themist generation material reduction equipment 20.

In this embodiment, by providing the second heat exchanger 33, the fluegas 12 is decreased to about, for example, 80 to 110° C., and thus theSO₃ gas is decreased to a sulfuric acid dew point or less and becomesmist-like SO₃. The mist-like SO₃ adheres to particulates in the flue gas12, and this is arrested by the electric dust collector 14 so as toreduce SO₃.

In this embodiment, as a result of converting SO₃ which is the mistgeneration material in the flue gas 12 from the gas state to the miststate and reducing the mist generation material in the mist state, adecrease in the amount of the SO₃ mist 50 introduced to the CO₂ recoveryequipment 17 is achieved. Therefore, the generation of white smoke ofthe purified gas 18 discharged from the CO₂ absorber 17A, which iscaused by the mist, is suppressed, and the entraining of the absorptionliquid 41 is suppressed. As a result, an air pollution control system inwhich the loss of the absorption liquid 41 is significantly decreasedmay be provided.

As described above in the embodiments, according to the presentinvention, since various forms of mist generation material reductionequipment 20 are provided, an air pollution control system in which theentraining of the absorption liquid 41 is significantly reduced when theflue gas 12 from which CO₂ is reduced is discharged to the outside ofthe system may be provided.

Even in various combinations of Embodiments 1 to 8, the effect of thepresent invention may be exhibited. Specifically, a combination of anyone of the sodium bisulfite injection equipment 21 of Embodiment 1, theammonia injection equipment 22 of Embodiment 2, and the dissolved saltspraying equipment 23 of Embodiment 3, and the wet type electric dustcollector 25 of Embodiment 4 and/or the demister 26 of Embodiment 6 maybe achieved.

In addition, a combination of any one of the sodium bisulfite injectionequipment 21 of Embodiment 1, the ammonia injection equipment 22 ofEmbodiment 2, and the dissolved salt spraying equipment 23 of Embodiment3 and the first heat exchanger 32 of Embodiment 7, and moreover, acombination of the former combination and the wet type electric dustcollector 25 of Embodiment 4 and/or the demister 26 of Embodiment 6 maybe achieved.

In addition, a combination of the second heat exchanger 33 of Embodiment8 and the wet type electric dust collector 25 of Embodiment 4 and/or thedemister 26 of Embodiment 6 may be achieved.

Here, it is preferable that the first and second heat exchangers 32 and33 not be general heat exchange members made of steel but be made of acorrosion-resistant material. This is because when SO₃ which is the mistgeneration material is changed from the gas state to the mist state,resistance to corrosion due to sulfurous acid or sulfuric acid isnecessary for long-term stable operation.

Here, as the corrosion-resistant material in the present invention, anacid-resistant organic material or inorganic material may be used. Forexample, as the organic material, “Teflon (registered trademark)” suchas polytetrafluoroethylene (PTFE) may be exemplified.

In this case, the constituent member of the heat exchanger may betreated by coating with the corrosion-resistant material, or theconstituent member itself may be manufactured of a corrosion-resistantmaterial.

REFERENCE SIGNS LIST

-   10, 10A to 10H AIR POLLUTION CONTROL SYSTEM-   11 Boiler-   12 Flue Gas-   13 NO_(x) Removal Equipment-   14 Electric Dust Collector-   15 SO_(x) Removal Equipment-   16 Cooler-   16 a Cooling Unit-   16 b Finishing SO_(x) Removal Unit-   17 CO₂ Recovery Equipment-   17A CO₂ Absorber-   17B Absorption Liquid Regenerator-   18 Purified Gas-   20 Mist Generation Material Reduction Equipment-   21 Sodium Bisulfite Injection Equipment-   22 Ammonia Injection Equipment-   23 Dissolved Salt Spraying Equipment-   24 Dissolved Salt-   25 Wet Type Electric Dust Collector-   25 a Wet Type Electric Dust Collection Unit-   26 Demister-   31 Calcium Carbonate Spraying Equipment-   32 First Heat Exchanger-   33 Second Heat Exchanger-   41 Absorption Liquid

1. An air pollution control system comprising: SO_(x) removal equipmentfor reducing sulfur oxides from flue gas from a boiler; a cooler whichis provided on a downstream side of the SO_(x) removal equipment forreducing the sulfur oxides that remain in the flue gas and fordecreasing a gas temperature; CO₂ recovery equipment including: a CO₂absorber for bringing CO₂ in the flue gas into contact with a CO₂absorption liquid so as to be reduced, and an absorption liquidregenerator for causing the CO₂ absorption liquid to emit CO₂ so as torecover CO₂ and regenerate the CO₂ absorption liquid; and mistgeneration material reduction equipment for reducing a mist generationmaterial which is a generation source of mist that is generated in theCO₂ absorber of the CO₂ recovery equipment before introducing the fluegas to the CO₂ recovery equipment.
 2. The air pollution control systemaccording to claim 1, further comprising: NO_(x) removal equipment forreducing nitrogen oxides from the flue gas; and a dry type electric dustcollector for reducing particulates.
 3. The air pollution control systemaccording to claim 2, wherein the mist generation material reductionequipment is a sodium bisulfite injection equipment for injecting sodiumbisulfite between the NO_(x) removal equipment and the electric dustcollector for reducing the mist generation material in a gas state fromthe flue gas.
 4. The air pollution control system according to claim 2,wherein the mist generation material reduction equipment is an ammoniainjection equipment for injecting ammonia to an upstream side of theelectric dust collector for reducing the mist generation material in agas state from the flue gas.
 5. The air pollution control systemaccording to claim 2, wherein the mist generation material reductionequipment is a dissolved salt spraying equipment for spraying adissolved salt between the electric dust collector and the SO_(x)removal equipment for reducing the mist generation material in a gasstate from the flue gas.
 6. The air pollution control system accordingto claim 1, wherein the mist generation material reduction equipment isa wet type electric dust collector which is provided on any of anupstream side and a downstream side of the cooler for reducingparticulates that remain in the flue gas and reducing the mistgeneration material in a mist state from the flue gas.
 7. The airpollution control system according to claim 1, wherein the mistgeneration material reduction equipment is a wet type electric dustcollector-integrated cooler which has a wet type electric dustcollection unit for reducing particulates that remain in the flue gastherein so as to reduce the mist generation material in a mist statefrom the flue gas.
 8. The air pollution control system according toclaim 1, wherein the mist generation material reduction equipment is ademister which is provided at a top portion of the cooler to reduceparticulates that remain in the flue gas therein the demister forreducing the mist generation material in a mist state from the flue gas.9. The air pollution control system according to claim 1, wherein themist generation material reduction equipment includes; a first heatexchanger which is provided on an upstream side of the SO_(x) removalequipment to decrease a temperature of the flue gas; and calciumcarbonate spraying equipment for spraying calcium carbonate between thefirst heat exchanger and the electric dust collector, and wherein themist generation material in the flue gas is converted from a gas stateto a mist state and the mist generation material in the mist state isneutralized using calcium carbonate so as to be reduced.
 10. The airpollution control system according to claim 2, wherein the mistgeneration material reduction equipment is a second heat exchanger whichis provided on an upstream side of the electric dust collector todecrease a temperature of the flue gas, and wherein the mist generationmaterial in the flue gas is converted from a gas state to a mist stateand the mist generation material in the mist state is adhered to theparticulates so as to be reduced by the dry type electric dustcollector.
 11. An air pollution control method comprising: on anupstream side of CO₂ recovery equipment for bringing CO₂ in flue gasinto contact with a CO₂ absorption liquid so as to be absorbed andreduced, reducing a mist generation material in any of a gas state and amist state from the flue gas generated in a boiler; and decreasing anamount of the mist generation material in the flue gas introduced to theCO₂ recovery equipment to a predetermined amount or less.